Aaron Alexis seems a study in contradictions: a former Navy reservist, a Defense Department contractor, a convert to Buddhism who was taking an online course in aeronautics. But he also had flashes of temper that led to run-ins with police over shootings in Fort Worth, Texas, and Seattle.

A profile began to emerge Monday of the man authorities identified as the gunman in a mass shooting at the Navy Yard in Washington, D.C., that left 13 people dead, including the 34-year-old man. While some neighbors and acquaintances described him as “nice,” his father once told detectives in Seattle that his son had anger management problems related to post-traumatic stress brought on by the terror attacks of Sept. 11, 2001. Alexis also complained to friends about the Navy and being a victim of discrimination.

At the time of the shootings, he worked for The Experts, a subcontractor on an HP Enterprise Services contract to refresh equipment used on the Marine Corps Intranet network.

His life over the past decade has been checkered.

Alexis lived in Seattle in 2004 and 2005, according to public documents. In 2004, Seattle police said, Alexis was arrested in 2004 for shooting out the tires of another man’s vehicle in what he later described to detectives as an anger-fueled “blackout.” According to an account on the department’s website, two construction workers had parked their Honda Accord in the driveway of their worksite, next to a home where Alexis was staying. The workers reported seeing a man, later identified by police as Alexis, walk out of the home next to their worksite, pull a gun from his waistband and fire three shots into the rear tires of their Honda before he walked slowly back to his home.

When detectives interviewed workers at the construction site, they told police Alexis had stared at construction workers at the job site daily for several weeks prior to the shooting. The owner of the construction business told police he believed Alexis was angry over the parking situation around the site.

Police eventually arrested Alexis, searched his home, found a gun and ammunition in his room, and booked him into the King County Jail for malicious mischief.

According to the police account, Alexis told detectives he perceived he had been “mocked” by construction workers the morning of the incident. Alexis also claimed he had an anger-fueled “blackout,” and could not remember firing his gun at the Honda until an hour after the incident.

Alexis also told police he was present during “the tragic events of Sept. 11, 2001″ and described “how those events had disturbed him.”

Then, on May 5, 2007, he enlisted in the Navy reserves, serving through 2011, according to Navy spokeswoman Lt. Megan Shutka.

Shutka said he received the National Defense Service Medal and the Global War on Terrorism Service Medal during his stint in the reserves. Both are medals issued to large numbers of service members who served abroad and in the United States since the 9/11 attacks. Alexis’ last assignment was as aviation electricians mate 3rd class at the Naval Air Station Joint Reserve Base in Fort Worth, Shutka said.

It was while he was still in the reserves that a neighbor in Fort Worth reported she had been nearly struck by a bullet shot from his downstairs apartment.

In September 2010, Fort Worth police questioned Alexis about the neighbor’s report; he admitted to firing his weapon but said he was cleaning his gun when it accidentally discharged. He said he didn’t call the police because he didn’t think the bullet went through to the other apartment. The neighbor told police she was scared of Alexis and felt he fired intentionally because he had complained about her making too much noise.

Alexis was arrested on suspicion of discharging a firearm within city limits but Tarrant County district attorney’s spokeswoman Melody McDonald Lanier said the case was not pursued after it was determined the gun discharged accidentally.

After leaving the reserves, Alexis worked as a waiter and delivery driver at the Happy Bowl Thai restaurant in White Settlement, a suburb of Fort Worth, according to Afton Bradley, a former co-worker. The two overlapped for about eight months before Alexis left in May, Bradley said.

Having traveled to Thailand, Alexis learned some Thai and could speak to Thai customers in their native language.

“He was a very nice person,” Bradley said in a phone interview. “It kind of blows my mind away. I wouldn’t think anything bad at all.”

A former acquaintance, Oui Suthametewakul, said Alexis lived with him and his wife from August 2012 to May 2013 in Fort Worth, but that they had to part ways because he wasn’t paying his bills. Alexis was a “nice guy,” Suthametewakul said, though he sometimes carried a gun and would frequently complain about being the victim of discrimination.

Suthametewakul said Alexis had converted to Buddhism and prayed at a local Buddhist temple.

“We are all shocked. We are nonviolent. Aaron was a very good practitioner of Buddhism. He could chant better than even some of the Thai congregants,” said Ty Thairintr, a congregant at Wat Budsaya, a Buddhist temple in Fort Worth.

Thairintr said Alexis told him he was upset with the Navy because “he thought he never got a promotion because of the color of his skin. He hated his commander.”

As Thairintr and others at the temple understood, Alexis took a job as a contractor and he indicated to them he was going to go to Virginia. He last saw him five weeks ago.

“He was a very devoted Buddhist. There was no tell-tale sign of this behavior,” Thairintr said.

In the early 2000s, before he moved to Seattle, Alexis lived with his mother in an apartment in the New York City borough of Queens, said Gene Demby, of Philadelphia, who said he dated one of Alexis’ younger sisters at the time. He said Alexis and his two younger sisters had a difficult relationship with their father, who divorced their mother in the mid-1990s.

“I wouldn’t call him nice, but he seemed harmless, if really awkward,” said Demby, the lead writer for National Public Radio’s Code Switch blog about race and culture. “He was insecure. He was like a barbershop conspiracy theorist, the kind of guy who believes he’s smarter than everyone else. He also was kind of like perpetually aggrieved, but not megalomaniacal or delusional.”

Embry-Riddle Aeronautical University, which offers online courses in aviation and aerospace, confirmed that Alexis was enrolled as an online student via its Fort Worth campus, started classes in July 2012 and was pursuing a bachelor’s of science in aeronautics.

“We are cooperating fully with investigating officials,” the university said.